```      SUBROUTINE ZHPR2(UPLO,N,ALPHA,X,INCX,Y,INCY,AP)
*     .. Scalar Arguments ..
DOUBLE COMPLEX ALPHA
INTEGER INCX,INCY,N
CHARACTER UPLO
*     ..
*     .. Array Arguments ..
DOUBLE COMPLEX AP(*),X(*),Y(*)
*     ..
*
*  Purpose
*  =======
*
*  ZHPR2  performs the hermitian rank 2 operation
*
*     A := alpha*x*conjg( y' ) + conjg( alpha )*y*conjg( x' ) + A,
*
*  where alpha is a scalar, x and y are n element vectors and A is an
*  n by n hermitian matrix, supplied in packed form.
*
*  Arguments
*  ==========
*
*  UPLO   - CHARACTER*1.
*           On entry, UPLO specifies whether the upper or lower
*           triangular part of the matrix A is supplied in the packed
*           array AP as follows:
*
*              UPLO = 'U' or 'u'   The upper triangular part of A is
*                                  supplied in AP.
*
*              UPLO = 'L' or 'l'   The lower triangular part of A is
*                                  supplied in AP.
*
*           Unchanged on exit.
*
*  N      - INTEGER.
*           On entry, N specifies the order of the matrix A.
*           N must be at least zero.
*           Unchanged on exit.
*
*  ALPHA  - COMPLEX*16      .
*           On entry, ALPHA specifies the scalar alpha.
*           Unchanged on exit.
*
*  X      - COMPLEX*16       array of dimension at least
*           ( 1 + ( n - 1 )*abs( INCX ) ).
*           Before entry, the incremented array X must contain the n
*           element vector x.
*           Unchanged on exit.
*
*  INCX   - INTEGER.
*           On entry, INCX specifies the increment for the elements of
*           X. INCX must not be zero.
*           Unchanged on exit.
*
*  Y      - COMPLEX*16       array of dimension at least
*           ( 1 + ( n - 1 )*abs( INCY ) ).
*           Before entry, the incremented array Y must contain the n
*           element vector y.
*           Unchanged on exit.
*
*  INCY   - INTEGER.
*           On entry, INCY specifies the increment for the elements of
*           Y. INCY must not be zero.
*           Unchanged on exit.
*
*  AP     - COMPLEX*16       array of DIMENSION at least
*           ( ( n*( n + 1 ) )/2 ).
*           Before entry with  UPLO = 'U' or 'u', the array AP must
*           contain the upper triangular part of the hermitian matrix
*           packed sequentially, column by column, so that AP( 1 )
*           contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 )
*           and a( 2, 2 ) respectively, and so on. On exit, the array
*           AP is overwritten by the upper triangular part of the
*           updated matrix.
*           Before entry with UPLO = 'L' or 'l', the array AP must
*           contain the lower triangular part of the hermitian matrix
*           packed sequentially, column by column, so that AP( 1 )
*           contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 )
*           and a( 3, 1 ) respectively, and so on. On exit, the array
*           AP is overwritten by the lower triangular part of the
*           updated matrix.
*           Note that the imaginary parts of the diagonal elements need
*           not be set, they are assumed to be zero, and on exit they
*           are set to zero.
*
*
*  Level 2 Blas routine.
*
*  -- Written on 22-October-1986.
*     Jack Dongarra, Argonne National Lab.
*     Jeremy Du Croz, Nag Central Office.
*     Sven Hammarling, Nag Central Office.
*     Richard Hanson, Sandia National Labs.
*
*
*     .. Parameters ..
DOUBLE COMPLEX ZERO
PARAMETER (ZERO= (0.0D+0,0.0D+0))
*     ..
*     .. Local Scalars ..
DOUBLE COMPLEX TEMP1,TEMP2
INTEGER I,INFO,IX,IY,J,JX,JY,K,KK,KX,KY
*     ..
*     .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
*     ..
*     .. External Subroutines ..
EXTERNAL XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC DBLE,DCONJG
*     ..
*
*     Test the input parameters.
*
INFO = 0
IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
INFO = 1
ELSE IF (N.LT.0) THEN
INFO = 2
ELSE IF (INCX.EQ.0) THEN
INFO = 5
ELSE IF (INCY.EQ.0) THEN
INFO = 7
END IF
IF (INFO.NE.0) THEN
CALL XERBLA('ZHPR2 ',INFO)
RETURN
END IF
*
*     Quick return if possible.
*
IF ((N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
*
*     Set up the start points in X and Y if the increments are not both
*     unity.
*
IF ((INCX.NE.1) .OR. (INCY.NE.1)) THEN
IF (INCX.GT.0) THEN
KX = 1
ELSE
KX = 1 - (N-1)*INCX
END IF
IF (INCY.GT.0) THEN
KY = 1
ELSE
KY = 1 - (N-1)*INCY
END IF
JX = KX
JY = KY
END IF
*
*     Start the operations. In this version the elements of the array AP
*     are accessed sequentially with one pass through AP.
*
KK = 1
IF (LSAME(UPLO,'U')) THEN
*
*        Form  A  when upper triangle is stored in AP.
*
IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
DO 20 J = 1,N
IF ((X(J).NE.ZERO) .OR. (Y(J).NE.ZERO)) THEN
TEMP1 = ALPHA*DCONJG(Y(J))
TEMP2 = DCONJG(ALPHA*X(J))
K = KK
DO 10 I = 1,J - 1
AP(K) = AP(K) + X(I)*TEMP1 + Y(I)*TEMP2
K = K + 1
10                 CONTINUE
AP(KK+J-1) = DBLE(AP(KK+J-1)) +
+                             DBLE(X(J)*TEMP1+Y(J)*TEMP2)
ELSE
AP(KK+J-1) = DBLE(AP(KK+J-1))
END IF
KK = KK + J
20         CONTINUE
ELSE
DO 40 J = 1,N
IF ((X(JX).NE.ZERO) .OR. (Y(JY).NE.ZERO)) THEN
TEMP1 = ALPHA*DCONJG(Y(JY))
TEMP2 = DCONJG(ALPHA*X(JX))
IX = KX
IY = KY
DO 30 K = KK,KK + J - 2
AP(K) = AP(K) + X(IX)*TEMP1 + Y(IY)*TEMP2
IX = IX + INCX
IY = IY + INCY
30                 CONTINUE
AP(KK+J-1) = DBLE(AP(KK+J-1)) +
+                             DBLE(X(JX)*TEMP1+Y(JY)*TEMP2)
ELSE
AP(KK+J-1) = DBLE(AP(KK+J-1))
END IF
JX = JX + INCX
JY = JY + INCY
KK = KK + J
40         CONTINUE
END IF
ELSE
*
*        Form  A  when lower triangle is stored in AP.
*
IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
DO 60 J = 1,N
IF ((X(J).NE.ZERO) .OR. (Y(J).NE.ZERO)) THEN
TEMP1 = ALPHA*DCONJG(Y(J))
TEMP2 = DCONJG(ALPHA*X(J))
AP(KK) = DBLE(AP(KK)) +
+                         DBLE(X(J)*TEMP1+Y(J)*TEMP2)
K = KK + 1
DO 50 I = J + 1,N
AP(K) = AP(K) + X(I)*TEMP1 + Y(I)*TEMP2
K = K + 1
50                 CONTINUE
ELSE
AP(KK) = DBLE(AP(KK))
END IF
KK = KK + N - J + 1
60         CONTINUE
ELSE
DO 80 J = 1,N
IF ((X(JX).NE.ZERO) .OR. (Y(JY).NE.ZERO)) THEN
TEMP1 = ALPHA*DCONJG(Y(JY))
TEMP2 = DCONJG(ALPHA*X(JX))
AP(KK) = DBLE(AP(KK)) +
+                         DBLE(X(JX)*TEMP1+Y(JY)*TEMP2)
IX = JX
IY = JY
DO 70 K = KK + 1,KK + N - J
IX = IX + INCX
IY = IY + INCY
AP(K) = AP(K) + X(IX)*TEMP1 + Y(IY)*TEMP2
70                 CONTINUE
ELSE
AP(KK) = DBLE(AP(KK))
END IF
JX = JX + INCX
JY = JY + INCY
KK = KK + N - J + 1
80         CONTINUE
END IF
END IF
*
RETURN
*
*     End of ZHPR2 .
*
END

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